The present invention relates to a semiconductor device and a serial data transmission line system and, for example, to a semiconductor device and a serial data transmission line system that relay transmission of serial data.
In recent years, high-speed serial communication that transmits high-speed serial data has been often used for data communication between devices. In this high-speed serial communication, deterioration of signal quality due to loss of a transmission line is largely concerned with communication quality. Consequently, as one of the methods that improve the communication quality, the following has been performed: characteristic change of the transmission line is detected using an adaptive equalizer circuit, and a correction value (for example, an equalizer coefficient) is dynamically adjusted so as to be able to receive data in a most suitable state.
Consequently, examples of the adaptive equalizer circuit are disclosed in Japanese Unexamined Patent Application Publication No. 2010-103974 and Japanese Unexamined Patent Application Publication No. 2005-191750. Japanese Unexamined Patent Application Publication No. 2010-103974 discloses a circuit configuration of the adaptive equalizer circuit.
In addition, in Japanese Unexamined Patent Application Publication No. 2005-191750, a technology of restarting a power supply when an error rate of an equalized signal obtained through an equalization unit exceeds a threshold value in a communication device having the equalization unit (for example, an equalizer circuit),is disclosed.
However, in order to improve a transmission speed of a signal in recent high-speed serial communication, a circuit is configured with a transistor formed in a fine process. The transistor formed in this fine process has a low breakdown withstand voltage, has a large voltage difference with respect to a voltage of an external power supply provided from outside, and needs to be made to operate with a power supply voltage lower than the voltage of the external power supply. Therefore, in a circuit utilized in the high-speed serial communication, an influence that a power supply noise has on signal quality is large, and there is a problem of being unable to obtain sufficient communication quality only by improvement of the signal quality by means of the adaptive equalizer circuit.
Other problems to be overcome by the present invention and new features thereof will be apparent from the description of the specification and accompanying drawings.